The target monitor is my 55" sony bravia LED tv.
Does it do good scanlines? Does it have the same kind of connectivity the other XRGBs have? Is it worth it over an XRGB1 or 2 if I want to use a big LED tv?
The Mini does scanlines, but the intensity is currently unadjustable. I don't use them myself, but people say they're "decent". This is something that may be addressed in a future firmware update. Google some screenshots and see what you think.
The mini has inputs for RGB, Composite, S-Video, HDMI and Component (over Japanese D-cable).
As far as I know all the older XRGBs can do VGA output, which may or may not look amazing on your HDTV, and may or may not have a lot of lag. The TV has to convert the analog VGA signal into digital to display it on the panel, and just like composite input, the quality varies by TV. This conversion process is the key point, and this is exactly what the Mini is for. It does all the converting, and lets you feed a digital signal from the HDMI cable right to the LCD with no additional muckery by the TV. (The mini has NO VGA support though, just to note).
The only way you're going to know if VGA input will work for you, is by testing your TV and a CRT monitor side-by-side. If it's not acceptable, you need a Mini. if it is, you can look into any of the older models. It would also be cool to get a hold of a video like the XRGB guys use in order to compare lag.